So I am seeing a number of reports from non- mainstream that NBC admits that an assault weapon was not used.

This is one from the independent Journal.
Pete Williams, who is NBC’s chief Justice correspondent, reported the following in the video posted above:

This continues to be a very complex investigation and there is a lot of contradictory information out there, but we have some new information this morning (one month ago) from a couple of federal officials and state officials.

They say now that there were actually four handguns inside the school, not just two as we were initially told. Four handguns and apparently only handguns that were taken into the school.

We knew that Adam Lanza, the man said to be the gunman here, also had an ‘assault-style’ AR-15 -style rifle that he had had taken to the school, it was in the car he drove there, his mother’s car, but we have been told by several officials that he had left that in the car.